1. Technical Field
Apparatuses and methods consistent with the present invention relate to minimizing hand-off time using mobile node information.
2. Related Art
As wired networking shifts to wireless networking, research on the dynamic combination of network devices is being conducted. A related art mobile Internet Protocol (IP) is an IP address provided to a mobile node.
FIG. 1 is a diagram showing an example of a related art process of assigning a mobile IP. A mobile node 100 moves to a foreign network 60 while communicating with a correspondent node 400 in a home domain 50 through a home agent 200. The mobile node 100 requests an L2 connection from an Access Point (AP) 301 in the foreign network 60. The AP 301 provides a response to the L2 connection request (as illustrated FIG. 2 and its accompanying disclosure) to the mobile node 100. Further, the movement of the mobile node 100 is detected through an advertisement message (a router advertisement), which is periodically transmitted by a router 500 or the AP 301. The mobile node generates a care-of address using the router advertisement. A Duplicate Address Detection (DAD) procedure starts to determine whether the care-of address is unique.
The DAD procedure is executed by transmitting a care-of address to another host or another node in a corresponding domain and determining whether a device using the same address as the care-of address exists. If a message indicating that the corresponding care-of address being used is received from the other device within a predetermined period of time (related art standards recommend 1 sec.), another care-of address is selected, and then a DAD procedure is re-executed. If a message, indicating that the corresponding care-of address being used is not received within the predetermined period of time, it is determined that the generated care-of address is unique and it is used. The mobile node 100 accordingly executes a Binding Update (BU) procedure to notify the home agent 200 and the correspondent node 400 that the IP of the mobile node 100 has changed.
FIG. 2 shows charts in which the time occupied by a hand-off delay time in a related art mobile IP is shown.
FIG. 2 includes a chart (a) showing the time from the point at which a mobile node leaves a previous link to the point at which the mobile node completes setup of a new link. In operation 1, a mobile node (MN) senses that it is starting to leave a previous link. Therefore, the setup of a new link starts in operation 2; from this time, hand-off starts. Further, if the setup of the new link is terminated in operation 4 after the previous link is deleted in operation 3, hand-off is completed. During a period starting from the point at which the previous link is deleted to the point at which the setup of the new link is terminated (i.e., the handoff delay), communication is not performed, and it is important to reduce such a period.
FIG. 2 also includes a chart (b) showing the hand-off time subdivided. The hand-off time is divided into L2 hand-off time and L3 hand-off time. The L2 hand-off time denotes the time for which hand-off in a Medium Access Control (MAC) Layer is performed; the L2 hand-off time is composed of periods for the operations of measuring a link, determining whether the link has changed, and performing hand-off if the link has changed.
The L3 hand-off time includes hand-off in a network layer, and it is composed of a movement detection period, an address conflict detection period and a Binding Update (BU) period. In order to detect movement, a period above 250 ms is required according to related art mobile IP related standards. If the period required for movement detection is short, there is an advantage in that movement can be promptly detected, but there is a disadvantage in that the burden on a router increases.
Address conflict detection period means the time required for the performance of the above-described DAD. If the DAD performance time is short, the hand-off time can be shortened. However, because the time required to detect a duplicate address is shortened, a minimum time of about 1000 ms is required by the standards. For the BU operation of indicating a changed address after the detection of an address conflict has terminated, about 10 ms is required.
In the case of typical voice data, if the hand-off time exceeds 150 ms, a user can detect the stoppage of service. Further, in the case of an application program more sensitive to time than voice data, if the hand-off is not processed within about 100 ms, service quality may deteriorate.
The L2 hand-off time is several tens of ms, but the L3 hand-off time requires about 1300 ms when the period recommended by the related art standards is obeyed, and this occupies most of the hand-off time. Therefore, there is a need to improve the performance of mobile IP is to minimize the hand-off time. In particular, a method and apparatus for reducing the address conflict detection period that occupies most of the L3 hand-off time are required.